Fix default mock_name in unittest.mock.assert_called error message

[tirkarthi]

BPO	37828
Nosy	@cjw296, @voidspace, @mariocj89, @pablogsal, @miss-islington, @tirkarthi
PRs	bpo-37828: Fix default mock_name in unittest.mock.assert_called error #16166 [3.8] bpo-37828: Fix default mock_name in unittest.mock.assert_called error (GH-16166) #16229

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2019-09-17.13:16:12.718>
created_at = <Date 2019-08-12.07:12:33.765>
labels = ['easy', '3.8', 'type-bug', 'library', '3.9']
title = 'Fix default mock_name in unittest.mock.assert_called error message'
updated_at = <Date 2019-09-17.13:16:12.717>
user = 'https://github.com/tirkarthi'

bugs.python.org fields:

activity = <Date 2019-09-17.13:16:12.717>
actor = 'xtreak'
assignee = 'none'
closed = True
closed_date = <Date 2019-09-17.13:16:12.718>
closer = 'xtreak'
components = ['Library (Lib)']
creation = <Date 2019-08-12.07:12:33.765>
creator = 'xtreak'
dependencies = []
files = []
hgrepos = []
issue_num = 37828
keywords = ['patch', 'newcomer friendly']
message_count = 4.0
messages = ['349444', '352629', '352631', '352635']
nosy_count = 6.0
nosy_names = ['cjw296', 'michael.foord', 'mariocj89', 'pablogsal', 'miss-islington', 'xtreak']
pr_nums = ['16166', '16229']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue37828'
versions = ['Python 3.8', 'Python 3.9']

[tirkarthi]

In the format string for assert_called the evaluation order is incorrect and hence for mock's without name 'None' is printed whereas it should be 'mock' like for other messages. The error message is ("Expected '%s' to have been called." % self._mock_name or 'mock') . Here self._mock_name which is None is applied to form the string and then used with the string 'mock' in or combination. The fix would be to have the evaluation order correct like other error messages. Marking this as newcomer-friendly. Please leave this to new contributors as their 1st PR.

./python.exe
Python 3.9.0a0 (heads/master:f03b4c8a48, Aug 12 2019, 10:04:10)
[Clang 7.0.2 (clang-700.1.81)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from unittest.mock import Mock
>>> m = Mock()
>>> m.assert_called_once()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/unittest/mock.py", line 854, in assert_called_once
    raise AssertionError(msg)
AssertionError: Expected 'mock' to have been called once. Called 0 times.
>>> m.assert_called()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/unittest/mock.py", line 844, in assert_called
    raise AssertionError(msg)
AssertionError: Expected 'None' to have been called.

Thanks

[pablogsal]

New changeset 5f5f11f by Pablo Galindo (Abraham Toriz Cruz) in branch 'master':
bpo-37828: Fix default mock_name in unittest.mock.assert_called error (GH-16166)
5f5f11f

[miss-islington]

New changeset f668d2b by Miss Islington (bot) in branch '3.8':
bpo-37828: Fix default mock_name in unittest.mock.assert_called error (GH-16166)
f668d2b

[tirkarthi]

I don't think 3.7 needs a backport of the fix. I am closing this as fixed since all PRs are merged. Please reopen if a backport is needed. Thanks @categulario.